The present application claims priority of Chinese patent application Ser. No. 200510123588.0, filed Nov. 21, 2005, the content of which is hereby incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to the radiographic field, and more particularly to a system and method for reconstructing an image by using a straight-line trajectory scan to improve the scan speed of a three-dimension stereography.
2. Description of the Prior Art
With the development of CT (computed tomography) techniques, a tomographic image with a certain quality can be reconstructed in a case of situation where a limited angle projection data is obtained or the data is truncated. Thus, it becomes practical to apply an incomplete scan and reconstruct approximate images. Theoretically, for an imaging system with a straight-line trajectory, if the length of scanning trajectory is infinite, an exact reconstruction could be achieved. If the trajectory is of a finite length, then it is equivalent to a limited-angle CT scan. Therefore, by using CT reconstructions dealing with incomplete data, cross-section images can be obtained from a straight-line imaging system, and the stereoscopic radiography is achieved.
In practical security inspections, fast custom clearance and rotation of large object are two difficulties. This is because in conventional CT imaging systems, we need either rotate the object to be inspected, or rotate the detector and the source while the object remains stationary. That is to say, it is difficult for large volume object to be inspected such as train and truck. Besides, a circular cone-beam scan has another drawback of large cone-angle problem.
With respect to the above problems, an imaging system having a straight-line trajectory, Computed Laminography system, has already been proposed. It has a small range of projection angles and tomosynthesis kinds of reconstruction algorithms are often used. Hence it is poor in three-dimension stereoscopic imaging capability and is thus not applied in the security inspections. To reconstruct an image from a straight-line trajectory, the rebinning-to-parallel-beam algorithm is a common choice, in which, projection data from the straight-line trajectory scan is rebinned into data under parallel beam scan and then the parallel beam filtered back-projection (FBP) reconstruction is carried out. However, this algorithm has a problem of low spatial resolution. This is because when the straight-line trajectory scanned data are rebinned into the parallel-beam scanned data, interpolations in the angular direction and the detector direction are needed and could reduce the spatial resolution in reconstructed images.